1. Field of the Invention
The present invention relates to a chuck for a machine tool, such as a lathe, and, more particularly, to a chuck having a chuck body and master jaws joined to the chuck body by spherical joints, i.e., the so-called swing lock chuck.
2. Description of the Related Art
A known swing lock chuck disclosed in, for example, JP-U No. 96106/1991 has main swing members (master jaws), respectively having middle spherical parts fitted in a part of a chuck body provided with spherical guide surfaces. The main swing members are supported for turning radially outward or radially inward relative to the chuck body about axis laterally extending past the centers of the spherical guide surfaces, respectively. A sliding tube (driving member) is axially slidably placed in the chuck body. A rotating member is supported for rotation by a support structure formed on the outer circumference of the sliding tube. A back end part of a main swing member is slidably inserted in an eccentric inclined hole formed in the rotating member. A recess is formed in the back end part of the main swing member. A pressing member (sliding member) is placed in the recess and is biased by a spring so as to be axially movable relative to the main swing member. The pressing member is pressed against a part of the chuck body facing the pressing member. As the sliding tube is reciprocated, the main swing member turns to open and close main clamping jaws (top jaws) supported on a front end part of the main swing member.
In this known chuck, a slight clearance is formed between the middle spherical parts of the master jaws and the spherical guide surfaces in a direction parallel to the axis of the chuck. Since the sliding member is pressed against the back end parts of the master jaws by the spring so as to be movable along the axis of the chuck, the master jaws turns radially inward and then master jaws move axially backward against the resilience of the spring when the driving member placed in the chuck body is retracted to move the master jaws radially inward. The backward movement of the master jaws does not cause any trouble at all when a workpiece is highly rigid, rather is desirable for drawing the workpiece toward a datum plane. When chucking a thin workpiece having a small dimension along the axis of the chuck, the backward movement of the master jaws bends the workpiece, which affects adversely to machining accuracy.
In such a case, the spring and the sliding member are replaced with other ones, a sliding member is attached fixedly to the back surfaces of the back end parts of the master jaws to eliminate the axial clearance between the middle spherical parts of the master jaws and the spherical guide surfaces so that the master jaws are unable to move axially and are able to move for opening and closing operations. However, the chuck must be disassembled and assembled every time the chuck is adjusted so that the master jaws may be able to move smoothly for opening and closing operations and sliding contact between the middle spherical parts and the spherical guide surfaces may not allow the backward movement of the master jaws because the sliding member is attached fixedly to the back surfaces of the back end parts of the master jaws. Thus, the known chuck requires very troublesome adjusting work.
Accordingly, it is an object of the present invention to provide a chuck including a chuck body and master jaws connected by spherical joints to the chuck body, and capable of facilitating adjusting work for adjusting the chuck so that the master jaws may not move backward along the axis of the chuck when chucking a workpiece even if a clearance is formed in the spherical joints.
According to one aspect of the present invention, a chuck comprises: a chuck body provided with a spherical guide surface; a master jaw mounted on the chuck body, the master jaw having a front end part, a back end part, and a middle spherical part extending between the front and the back end part and guided by the spherical guide surface, and the master jaw being provided with a through hole extending through the front end part, the middle spherical part and the back end part; a top jaw mounted on the front end part of the master jaw; a driving member slidably supported in the chuck body and connected by a spherical bearing member to the back end part of the master jaw to turn the master jaw on the middle spherical part engaged in the spherical guide surface when moved in the chuck body; a stopper mounted on the chuck body opposite to the back end part of the master jaw; and a sliding member inserted in the through hole of the master jaw, the sliding member having a back end part in sliding contact with the stopper so as to limit movement of the master jaw in a direction parallel to an axis of the chuck body when the mater jaw is turned.
In this chuck, it is preferable that the through hole of the master jaw has a counterbored section formed in the front end part of the master jaw and opening in a part to which the top jaw is attached, a bored section formed in the back end part of the master jaw, and an internally threaded section extending between the counterbored section and the bored section; and the movement of the sliding member fitted in the bored section is limited by a bolt having a head and screwed in the internally threaded section.
In this chuck, it is preferable that a spacer is interposed between the bottom surface of the counterbored section and the head of the bolt screwed in the internally threaded section.
In this chuck, it is preferable that the stopper is a highly abrasion-resistant member attached to the chuck body.
In this chuck, it is preferable that a surface of the back end part of the sliding member, in sliding contact with the stopper has a circular shape having its center at the center of the middle spherical part of the master jaw.
According to the present invention, the master jaw is provided with the through hole extending between the front to the back end thereof and the sliding member is inserted in the through hole of the master jaw through the front end of the through hole so as to come into sliding contact with the stopper attached to the chuck body. Therefore, the state of sliding contact between the sliding member and the stopper can be adjusted on the side of the front part of the chuck, the chuck does not need to be disassembled and assembled for the adjustment of the state of sliding contact, and work for adjusting the state of sliding contact can be easily achieved.
According to the present invention, the through hole of the master jaw has the counterbored section formed in the front end part of the master jaw and opening in the part to which the top jaw is attached, the bored section formed in the back end part of the master jaw, and the internally threaded section extending between the counterbored section and the bored section, and hence the sate of sliding contact between the sliding member and the stopper can be simply and properly adjusted by interposing a spacer having a proper thickness between the head of the bolt screwed in the internally threaded section and the bottom surface of the counterbored section.
According to the present invention, the highly abrasion-resistant member is attached to the chuck body to form the stopper, and hence the durability of the chuck can be improved.
Since the surface of the back end part of the sliding member, in sliding contact with the stopper has the circular shape having its center at the center of the middle spherical part of the master jaw, the sliding member does not obstruct the turning motion of the master jaw even though the sliding member is in sliding contact with the stopper.